Estimated reading time 5 minutes, 35 seconds.
Since 1958, Carson Helicopters of Perkasie, Pennsylvania, has been delivering a suite of products and services to support the helicopter industry, primarily focusing on the Sikorsky S-61 and SH-3 Sea King.
In 2003, the company received approval for its composite S-61 main rotor blade, which gives the helicopter about 1,750 pounds (793 kg) of additional lift capability under hot and high conditions.
Then, in April of 2018, Carson Helicopters received its initial supplemental type certificate (STC) for its composite S-61 tail rotor blades.
“Typically, as part of a composite blade STC project, we break it up into segments. Our first STC is just to install the new blade,” explained company vice president, Clayton Carson. “We don’t go after performance improvements initially; instead, we look at matching performance to the existing [metal] blades. Once that is successful, we go for performance improvements, which simplifies the initial project and helps make it go more smoothly.”
Since receiving the S-61 composite tail rotor STC, Carson Helicopters has made further improvements, recently gaining U.S. Federal Aviation Administration (FAA) certification for an additional 150 pounds (68 kg) of lift at an altitude of 7,000 feet (2,133 meters) and temperatures of 68 F (20 C). The new composite tail rotor blades also increase the max gross weight altitude by approximately 1,000 feet (304 meters).
The company says composite blades deliver a number of operational advantages.
“Compared to the metal blades, they offer better damage tolerance, better performance, and reduced maintenance,” explained Carson.
“Composite blades give us a lot more freedom of design compared to a metal extrusion spar, and that lets us use different types of airfoils. We can really cater the airfoil and twist along the span of the blade, and that’s really where you get improved performance. Or, you can make it slightly quieter with an optimized tip design, for example.”
The Carson Helicopters S-61 composite tail rotor blade features cambered airfoils with an eight-degree twist. These airfoils, which are the same as those used in the company’s main rotor blades, provide greater performance while maintaining the unique advantages of composites, including improved damage tolerance.
Carson said that if a crack develops in a metal blade, it can spread quickly and could cause a failure if not detected. Composites, on the other hand, are by design more robust and more tolerant of small damage or cracks. Additionally, they are resistant to corrosion.